A sequence of numbers, such as 1, 1, 2, 3, 5, 8, 13 ... , in which each successive number is equal to the sum of the two preceding numbers. Many shapes occurring in nature, such as certain spirals, have proportions that can be described in terms of the Fibonacci sequence. See also golden section.

mathematics The infinite sequence of numbers beginning 1, 1, 2, 3, 5, 8, 13, ... in which each term is the sum of the two terms preceding it. The ratio of successive Fibonacci terms tends to the golden ratio, namely (1 + sqrt 5)/2. [Why not "Fibonacci series"?] (2002-10-15)